Read and write negative intervals

[alaricd]

DuckDB intervals can be negative: duckdb_interval.micros is int64_t, and days can be negative too. DuckDBInterval converted both as unsigned, so today, on develop:

cmd.CommandText = "SELECT INTERVAL '-90 minutes'";
reader.GetFieldValue<TimeSpan>(0); // ArgumentOutOfRangeException: "...total microseconds is larger than 9223372036854775807"

• reading any negative interval as a TimeSpan throws, even INTERVAL '-2 days' (zero micros);
• INTERVAL '-1 month' reads as 00:00:00: the negative month is silently dropped, while +1 month throws;
• binding or appending a negative TimeSpan throws OverflowException ("Value was either too large or too small for a UInt64").

Change

• ToTimeSpan reads Micros as its signed value, adds days and micros in Int128, and refuses a result outside TimeSpan's range. A non-zero month count of either sign is refused instead of dropped.
• FromTimeSpan keeps the sign: Days is the whole days of the TimeSpan and Micros the signed remainder, truncated toward zero.
• Micros stays a ulong so the public API doesn't change; the value is its two's complement. (A long would be the natural type for a future major version.)

Tests

• DuckDBIntervalTests: negative micros, negative and mixed-sign days, a negative month, the range limit, and negative TimeSpan → interval. The existing tests are unchanged and still pass.
• Parameters/IntervalTests (new): SELECT INTERVAL '...' for negative and mixed-sign values through GetValue and GetFieldValue<TimeSpan>; a negative TimeSpan parameter inserted into an INTERVAL column and compared with CAST('n microseconds' AS INTERVAL); the appender writing a negative TimeSpan; ±1 month refused as a TimeSpan.
• The new tests fail on develop (17 of them) and pass with the change, 5/5 runs. Full suite: 7175 passed against DuckDB 1.5.6 (Linux x64, net8.0).

Not in this PR

A TimeSpan parameter whose target type DuckDB can't infer (for example SELECT ?::INTERVAL) is sent as TimeSpan.ToString(), because TimeSpan has no DbType mapping. DuckDB parses -01:30:00, but not the 1.01:01:01 form .NET uses once there are days, positive or negative. The new tests bind into a typed column to stay clear of it; happy to open a separate issue or PR.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟢 Approval recommended

The signed conversions are correct, range-safe, and comprehensively covered by focused tests.

Review effort: Balanced
Findings: None

What changed in this PR

Corrects interval conversion in the native bindings to support negative days and microseconds safely.

Changes:

• Uses signed two’s-complement microseconds and Int128 range checking.
• Preserves negative TimeSpan values during parameter and appender writes.
• Adds unit and integration coverage for negative, mixed-sign, monthly, and out-of-range intervals.

File	Description
DuckDB.NET.Bindings/​DuckDBInterval.cs	Corrects signed interval conversion and range validation.
DuckDB.NET.Test/​DuckDBIntervalTests.cs	Tests conversion boundaries and negative values.
DuckDB.NET.Test/​Parameters/​IntervalTests.cs	Tests querying, binding, and appending negative intervals.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.94%. Comparing base (56b8941) to head (f9de56d).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #359      +/-   ##
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+ Coverage    89.89%   89.94%   +0.05%     
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  Files           82       82              
  Lines         3583     3572      -11     
  Branches       557      553       -4     
===========================================
- Hits          3221     3213       -8     
+ Misses         231      230       -1     
+ Partials       131      129       -2     

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[coveralls]

Coverage Report for CI Build 37478637040

Coverage increased (+0.03%) to 91.69%

Details

• Coverage increased (+0.03%) from the base build.
• Patch coverage: 7 of 7 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

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Coverage Regressions

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Coverage Stats

Relevant Lines:	3572
Covered Lines:	3342
Line Coverage:	93.56%
Relevant Branches:	1855
Covered Branches:	1634
Branch Coverage:	88.09%
Branches in Coverage %:	Yes
Coverage Strength:	419310.55 hits per line

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[Giorgi]

Thanks, this looks good. I checked it on Windows as well, and against develop the old code is worse than the description says: INTERVAL '-1 year 2 days' reads as 2.00:00:00, with the year silently dropped.

A few cases beyond the tests in the PR also behave correctly with the change:

• TimeSpan.MinValue and TimeSpan.MaxValue round-trip through an INTERVAL column (to the microsecond). On develop both fail, including the positive one.
• INTERVAL '-1 day 25 hours' reads as 01:00:00.
• TIMESTAMP '2020-01-01' - TIMESTAMP '2021-03-05' reads as -429.00:00:00.
• Intervals outside TimeSpan's range throw ArgumentOutOfRangeException and still read as DuckDBInterval.

Yes, please open a separate PR for the item under "Not in this PR": a TimeSpan parameter with no target type being sent as TimeSpan.ToString().